The present invention relates to glyph codes, and in particular to glyph codes having occluded regions.
Codes can be embedded in an image on a substrate using machine-readable marks, such as glyph marks used in Xerox DATAGLYPH codes. The machine-readable marks can be captured in an image, and the image analyzed to extract information from the codes embedded in the image. Glyph marks in particular have several advantages. For example, glyph codes can be decoded from glyph marks even when the image carrying the glyph marks is distorted or there is some type of noise in the glyph marks.
Another advantage of glyph marks is that they may have an unobtrusive visual appearance. If the glyph marks are sufficiently small, the glyphs appear as grayscale to the unaided eye. For example, logically-ordered, single-bit digital quanta may be encoded by respective elongated slash-like glyphs tilted to the left and right of vertical by approximately +45° and −45° for encoding logical “0s” and “1s,” respectively. The mutual orthogonality of the glyphs for the two logical states of 0 and 1 of these single bit digital quanta enhances the discriminability of the code. Thus, the code pattern embedded in the glyphs can be recovered from an image of the glyphs, even when the code pattern is written on a fine grain pattern to cause the code pattern to have a generally uniform grayscale appearance.
Decoding machine-readable marks, such as glyphs, in a substrate image requires an image capture window sized large enough to capture a sufficiently large set of glyphs from which the code pattern embedded therein can be decoded. If the capture area is too small, there will not be a sufficiently large set of glyph codes from which the embedded code pattern can be decoded. Therefore, the required size and shape of the image capture window will vary depending on the particular code pattern embedded in the glyphs and the characteristics of the glyphs, such as size, shape, and orientation. For periodic tiled glyph patterns, an image capture window encompassing a tile provides an image area of glyphs that can be used for glyph decoding. If the capture window is shifted from alignment with a tile in a periodic tiled code pattern, the tile can still be reconstructed from the captured parts. See, for example, U.S. Pat. No. 6,000,621 to Hecht, et al., entitled Tilings of Mono-Code and Dual-Code Embedded Data Pattern Strips For Robust Asynchronous Capture, which teaches facilitating recovery of data through use of an appropriately-sized capture window, and is hereby expressly incorporated by reference. Once a complete tile has been captured, it can be decoded and the retrieved information used to perform a function.
Unfortunately, prior art tiled code systems are somewhat limited in their use as graphical printing occlusions may obscure parts of a tile needed for decoding. What is needed is a code system that enables use with graphical occlusions. It is also desirable that the code system accommodate additional code elements such as address codes to provide more information in addition to that found in prior art tiled code systems.
It is sometimes additionally desirable to occlude areas of the substrate with graphical markings that may interfere with data glyph reading. For example, in a system implementing a graphical user interface on a substrate, graphics, such as icons, may occlude glyphs on the substrate. The user places an image capture device over an area of the substrate to select an icon. The image captured by the image capture device typically includes regions where glyph codes are occluded. Conventional codes may not provide robust decoding because they are not designed to compensate for the occlusions.
What is needed is a code system that allows for occluded areas of glyphs and still provides a robust decoding of the underlying glyphs captured by an image capture device having a limited window capture size.